Disk array enclosure with metadata journal

ABSTRACT

A storage system comprises a disk array enclosure comprising an enclosure controller, a cache comprising a metadata journal, a plurality of data storage devices and a plurality of metadata storage devices. The enclosure controller is configured to write a stripe metadata page to the metadata storage devices that corresponds to a stripe of data stored on the data storage devices and to determine that the write of the stripe metadata page failed for a first metadata storage device. The enclosure controller is configured to add an entry to the metadata journal based on the determination that the write failed. The entry comprises an indication of the first metadata storage device and the stripe of data. The enclosure controller is configured to set an indication in a data structure associated with the disk array enclosure that the stripe metadata page has not been written to the first metadata storage device.

FIELD

The field relates generally to information processing systems, and moreparticularly to storage in information processing systems.

BACKGROUND

In a typical information processing system, host devices interface witha storage system comprising controllers and storage devices to performdata storage related operations. For example, applications executing onthe host devices may issue input-output (TO) operations to the storagesystem which request that data be written to or read from the storagedevices. The controllers receive these IO operations and interact withthe storage devices to perform the IO operations. The storagecontrollers then return the results of the IO operations to the hostdevices.

SUMMARY

In some embodiments, a storage system comprises a disk array enclosure.The disk array enclosure comprises at least one enclosure controllercomprising at least one processing device coupled to memory. The diskarray enclosure further comprises a cache comprising a metadata journaland a plurality of data storage devices in communication with the atleast one enclosure controller. The disk array enclosure furthercomprises a plurality of metadata storage devices in communication withthe at least one enclosure controller. Each metadata storage device isconfigured to store metadata corresponding to data stored on theplurality of storage devices. The at least one enclosure controller isconfigured to write a stripe metadata page to the metadata storagedevices. The stripe metadata page corresponds to a stripe of data storedon the plurality of data storage devices of the disk array enclosure.The at least one enclosure controller is further configured to determinethat the write of the stripe metadata page failed for a first metadatastorage device of the plurality of metadata storage devices and to addan entry to the metadata journal based at least in part on thedetermination that the write of the stripe metadata page failed. Theentry comprises an indication of the first metadata storage device andan indication of the stripe of data. The at least one enclosurecontroller is further configured to set an indication in a datastructure associated with the disk array enclosure that the stripemetadata page for the stripe of data has not been written to the firstmetadata storage device.

These and other illustrative embodiments include, without limitation,apparatus, systems, methods and processor-readable storage media.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one example of an information processingsystem within which one or more illustrative embodiments areimplemented.

FIG. 2 is a block diagram of an example disk array enclosure of theinformation processing system of FIG. 1 within which one or moreillustrative embodiments are implemented.

FIG. 3 is a block diagram of one example of a RAID arrangement withinwhich one or more illustrative embodiments are implemented.

FIG. 4 is a flow diagram illustrating an example technique foroffloading of a write operation in an illustrative embodiment.

FIG. 5 is a flow diagram illustrating an example technique foroffloading of a read operation in an illustrative embodiment.

FIG. 6 is a flow diagram illustrating an example technique foroffloading metadata storage device management functionality in anillustrative embodiment.

FIG. 7 is a flow diagram illustrating an example technique foroffloading in an illustrative embodiment.

FIG. 8 shows a content addressable storage system configured withfunctionality for offloading in an illustrative embodiment.

FIGS. 9 and 10 show examples of processing platforms that may beutilized to implement at least a portion of an information processingsystem in illustrative embodiments.

DETAILED DESCRIPTION

Illustrative embodiments will be described herein with reference toexemplary information processing systems and associated computers,servers, storage devices and other processing devices. It is to beappreciated, however, that these and other embodiments are notrestricted to the particular illustrative system and deviceconfigurations shown. Accordingly, the term “information processingsystem” as used herein is intended to be broadly construed, so as toencompass, for example, processing systems comprising cloud computingand storage systems, as well as other types of processing systemscomprising various combinations of physical and virtual processingresources. An information processing system may therefore comprise, forexample, at least one data center or other cloud-based system thatincludes one or more clouds hosting multiple tenants that share cloudresources. Numerous different types of enterprise computing and storagesystems are also encompassed by the term “information processing system”as that term is broadly used herein.

FIG. 1 shows an information processing system 100 configured inaccordance with an illustrative embodiment. The information processingsystem 100 comprises a computer system 101 that includes host devices102-1, 102-2, . . . 102-J collectively referred to as host devices 102.The host devices 102 communicate over a network 104 with a storagesystem 105. The computer system 101 is assumed to comprise an enterprisecomputer system, cloud-based computer system or other arrangement ofmultiple compute nodes associated with respective users. The hostdevices 102 of the computer system 101 in some embodimentsillustratively provide compute services such as execution of one or moreapplications on behalf of each of one or more users associated withrespective ones of the host devices 102.

The host devices 102 and storage system 105 illustratively compriserespective processing devices of one or more processing platforms. Forexample, the host devices 102 and the storage system 105 can eachcomprise one or more processing devices each having a processor and amemory, possibly implementing virtual machines and/or containers,although numerous other configurations are possible.

The host devices 102 and the storage system 105 can additionally oralternatively be part of cloud infrastructure such as an Amazon WebServices (AWS) system. Other examples of cloud-based systems that can beused to provide one or more of host devices 102 and the storage system105 include Google Cloud Platform (GCP) and Microsoft Azure.

The host devices 102 are configured to write data to and read data fromthe storage system 105. The host devices 102 and the storage system 105may be implemented on a common processing platform, or on separateprocessing platforms. A wide variety of other types of host devices canbe used in other embodiments.

The host devices 102 in some embodiments illustratively provide computeservices such as execution of one or more applications on behalf of eachof one or more users associated with the host devices 102.

The term “user” herein is intended to be broadly construed so as toencompass numerous arrangements of human, hardware, software or firmwareentities, as well as combinations of such entities. Compute and/orstorage services may be provided for users under a Platform-as-a-Service(PaaS) model, although it is to be appreciated that numerous other cloudinfrastructure arrangements could be used. Also, illustrativeembodiments can be implemented outside of the cloud infrastructurecontext, as in the case of a stand-alone computing and storage systemimplemented within a given enterprise.

The network 104 is assumed to comprise a portion of a global computernetwork such as the Internet, although other types of networks can bepart of the network 104, including a wide area network (WAN), a localarea network (LAN), a satellite network, a telephone or cable network, acellular network, a wireless network such as a WiFi or WiMAX network, orvarious portions or combinations of these and other types of networks.The network 104 in some embodiments therefore comprises combinations ofmultiple different types of networks each comprising processing devicesconfigured to communicate using Internet Protocol (IP) or othercommunication protocols.

As a more particular example, some embodiments may utilize one or morehigh-speed local networks in which associated processing devicescommunicate with one another utilizing Peripheral Component Interconnectexpress (PCIe) cards of those devices, and networking protocols such asInfiniBand, Gigabit Ethernet, Fibre Channel, or Non-Volatile Memoryexpress Over Fabrics (NVMeOF). Numerous alternative networkingarrangements are possible in a given embodiment, as will be appreciatedby those skilled in the art.

The storage system 105 is accessible to the host devices 102 over thenetwork 104. The storage system 105 comprises a disk array enclosure106, a storage controller 108, and an associated cache 109. In someembodiments, the storage controller 108 and cache 109 may be optionalwhere, for example, the storage system 105 may comprise the disk arrayenclosure 106 without also comprising the storage controller 108 orcache 109. In some embodiments, more than one disk array enclosure 106,storage controller 108 or cache 109 may be included in storage system105. The term “disk array enclosure” as used herein is intended to bebroadly construed, so as to encompass an enclosure comprising, forexample, any form of memory or storage device including, storage classmemory, flash drives, solid state drives, hard disk drives, hybriddrives or other types of storage devices.

With reference to FIGS. 1 and 2, the disk array enclosure 106illustratively comprises data storage devices 110, metadata storagedevices 112, enclosure controllers 114, network devices 116, memory 118,cache 120 and offload logic 122. An example of disk array enclosure 106is illustrated in FIG. 2.

Data storage devices 110, also referred to in FIG. 2 as DSDs 110-1,110-2, 110-3 . . . 110-S-1, 110-S, may comprise, for example, solidstate drives (SSDs). Such SSDs are implemented using non-volatile memory(NVM) devices such as flash memory. Other types of NVM devices that canbe used to implement at least a portion of the data storage devices 110include non-volatile random-access memory (NVRAM), phase-change RAM(PC-RAM) and magnetic RAM (MRAM). These and various combinations ofmultiple different types of NVM devices may also be used.

Metadata storage devices 112, also referred to in FIG. 2 as MSDs 112-1,112-2 and 112-3, may comprise any of the storage devices described abovefor data storage devices 110. In some embodiments, metadata storagedevices 112 may comprise higher grade storage devices than the datastorage devices 110. For example, the metadata storage devices 112 mayhave higher bandwidth and lower latency characteristics than the datastorage device 110. In some embodiments, for example, metadata storagedevices 112 may comprise storage class memory (SCM) storage deviceswhile the data storage devices 110 may comprise NVM express (NVMe)storage devices or other storage devices that have smaller bandwidth orhigher latency than SCM storage devices. In other embodiments, bothmetadata storage devices 112 and data storage devices 110 may comprisethe same class of memory, e.g., SCM, NVMe, etc., with the metadatastorage devices 112 having improved bandwidth and latencycharacteristics as compared to the data storage devices 110. While onlythree MSDs 112 are illustrated in FIG. 2, any other number of MSDs 112may be used in other embodiments.

It is to be appreciated that other types of data storage devices 110 andmetadata storage devices 112 can be used in other embodiments. Forexample, a given storage system 105 as the term is broadly used hereincan include a combination of different types of data storage devices, asin the case of a multi-tier storage system comprising a flash-based fasttier and a disk-based capacity tier. In such an embodiment, each of thefast tier and the capacity tier of the multi-tier storage systemcomprises a plurality of data storage devices with different types ofdata storage devices being used in different ones of the storage tiers.For example, the fast tier may comprise flash drives while the capacitytier comprises hard disk drives. The particular data storage devicesused in a given storage tier may be varied in other embodiments, andmultiple distinct data storage device types may be used within a singlestorage tier. Likewise, in some embodiments, a fastest tier of thestorage system may comprise the metadata storage devices 112. The terms“storage device” and “disk” as used herein are intended to be broadlyconstrued, so as to encompass, for example, storage class memory, flashdrives, solid state drives, hard disk drives, hybrid drives or othertypes of storage devices.

Enclosure controllers 114, e.g., enclosure controllers 114-1 and 114-2as shown in the example disk array enclosure 106 of FIG. 2, comprise oneor more processing devices such as, e.g., microprocessors,microcontrollers, application-specific integrated circuits (ASICs),field-programmable gate arrays (FPGAs), graphics processing units (GPUs)or other types of processing circuitry, as well as portions orcombinations of such circuitry elements. In illustrative embodiments,enclosure controllers 114 are less powerful than storage controller 108.For example, enclosure controllers 114 may comprise less processingpower than storage controller 108. In some cases, enclosure controllers114 may comprise significantly less processing power than storagecontrollers 108. For example, a given enclosure controller 114 maycomprise less than 75%, 50%, 25% or any other percent of the processingpower of the storage controller 108.

Enclosure controllers 114 communicate with the rest of the components ofstorage array 105 or with computer system 101 via one or moreconnections 126, e.g., connections 126-1, 126-2, 126-3 and 126-4 in theexample of FIG. 2. Connections 126 may comprise wired or wirelesscommunication methods and components or any other communication mediumwhich allows the enclosure controllers 114 to communicate with one ormore of host devices 102, storage controller 108, cache 109, or anyother component of system 100. As an example, in some embodiments,connections 126 may comprise ethernet or other wired connections whicheach provide at least 50 Gbps of data bandwidth to the enclosurecontrollers 114. Connections 126 providing a larger or smaller bandwidththan 50 Gbps may also or alternatively be utilized.

Network devices 116, e.g., network devices 116-1 and 116-2 as shown inthe example disk array enclosure 106 of FIG. 2, comprise, for example,PCIe switches or other network components that facilitate communicationbetween enclosure controllers 114-1 and 114-2, data storage devices110-1, 110-2, 110-3 . . . 110-S-1, 110-S, and metadata storage devices112-1, 112-2 and 112-3.

Memory 118, e.g., memory 118-1 and 118-2 as shown in the example diskarray enclosure 106 of FIG. 2, may comprise volatile memory such as,e.g., random access memory (RAM), dynamic random-access memory (DRAM),static random-access memory (SRAM), or any other kind of volatilememory. In some embodiments, memory 118 may additionally oralternatively comprise any non-volatile memory as described above withrespect to data storage devices 110. While illustrated as separatecomponents of disk array enclosure 106, in some embodiments, a separatememory 118 may be included as a component of each of the enclosurecontrollers 114-1 and 114-2

The cache 120 of disk array enclosure 106 comprises a metadata journal124 which comprises entries associated with failed metadata writes tothe metadata storage devices 112 for later hardening to the metadatastorage devices 112 of the disk array enclosure 106. In illustrativeembodiments, cache 120 comprises persistent memory such as, e.g., anynon-volatile memory as described above with respect to data storagedevices 110. In other embodiments, cache 120 may illustratively comprisevolatile memory such as, e.g., random access memory (RAM), dynamicrandom-access memory (DRAM), static random-access memory (SRAM), or anyother kind of volatile memory. While illustrated as a separate componentof disk array enclosure 106, in some embodiments, cache 120 may beincluded as a component of one or more of the enclosure controllers114-1 and 114-2.

Storage controller 108 comprises one or more processing devices such as,e.g., microprocessors, microcontrollers, application-specific integratedcircuits (ASICs), field-programmable gate arrays (FPGAs), graphicsprocessing units (GPUs) or other types of processing circuitry, as wellas portions or combinations of such circuitry elements. As mentionedabove, in illustrative embodiments, the storage controller 108 may havea greater processing power than the enclosure controllers 114 of thedisk array enclosure 106.

The cache 109 of storage system 105 in the FIG. 1 embodiment includescache entries which store incoming input-output (10) request data forlater destaging to storage devices of the storage enclosures 106. Cache109 may illustratively comprise volatile memory such as, e.g., randomaccess memory (RAM), dynamic random-access memory (DRAM), staticrandom-access memory (SRAM), or any other kind of volatile memory. Insome embodiments, cache 109 may additionally or alternatively compriseany non-volatile memory as described above with respect to disk arrayenclosure 106. In some embodiments, cache 109 may support a variety ofoperations or functions of storage system 105 including, for example,write cache, read cache, or other similar operations. While illustratedas a separate component of storage system 105, in some embodiments,cache 109 may be included as a component of storage controller 108. Insome embodiments, where multiple storage controllers 108 each comprisinga separate cache 109 are implemented, the caches 109 of the storagecontrollers 108 may operate together as a single cache 109 where thecomponents of a given storage system 105 may access any portion of thecache 109 including those portions included as components of otherportions of storage system 105.

In some embodiments, the storage system 105 illustratively comprises ascale-out all-flash content addressable storage array such as anXtremIO™ storage array from Dell EMC of Hopkinton, Mass. Other types ofstorage arrays, including by way of example VNX® and Symmetrix VMAX®storage arrays also from Dell EMC, can be used to implement storagesystem 105 in other embodiments.

The term “storage system” as used herein is therefore intended to bebroadly construed, and should not be viewed as being limited to contentaddressable storage systems or flash-based storage systems. A givenstorage system as the term is broadly used herein can comprise, forexample, network-attached storage (NAS), storage area networks (SANs),direct-attached storage (DAS) and distributed DAS, as well ascombinations of these and other storage types, includingsoftware-defined storage.

Other particular types of storage products that can be used to implementstorage system 105 in illustrative embodiments include all-flash andhybrid flash storage arrays such as Unity™, software-defined storageproducts such as ScaleIO™ and ViPR®, cloud storage products such asElastic Cloud Storage (ECS), object-based storage products such asAtmos®, and scale-out NAS clusters comprising Isilon® platform nodes andassociated accelerators, all from Dell EMC. Combinations of multipleones of these and other storage products can also be used inimplementing a given storage system in an illustrative embodiment.

In an illustrative embodiment, as illustrated in FIGS. 1 and 2, the diskarray enclosure 106 includes offload logic 122, e.g., offload logic122-1 and 122-2 as shown in the example disk array enclosure 106 of FIG.2, which provides logic and functionality for offloading some or all ofthe RAID processing of data pages from the storage controller 108 to theenclosure controllers 114 of the disk array enclosure 106. Theoffloading of the RAID processing may comprise, for example, write flow,compression and error offloading. Offload logic 122 also provides logicand functionality for offloading the mapping of logical identifiers,such as, e.g., content-based signatures, to the corresponding physicallocations on the data storage devices 110 that store the data associatedwith the logical identifiers. By offloading this processingfunctionality to the enclosure controllers 114 of the disk arrayenclosures 106, the availability of storage controller 108 for servicingadditional input-output operations is increased. The offload logic 122will be described in more detail below.

The host device 102 should also be understood to include additionalmodules and other components typically found in conventionalimplementations of computers, servers or other host devices, althoughsuch additional modules and other components are omitted from the figurefor clarity and simplicity of illustration.

The host device 102 and storage system 105 in the FIG. 1 embodiments areassumed to be implemented using at least one processing platform eachcomprising one or more processing devices each having a processorcoupled to a memory. Such processing devices can illustratively includeparticular arrangements of compute, storage and network resources.

The host devices 102 and the storage system 105 may be implemented onrespective distinct processing platforms, although numerous otherarrangements are possible. For example, in some embodiments at leastportions of the host devices 102 and at least portions of the storagesystem 105 are implemented on the same processing platform. The storagesystem 105 can therefore be implemented at least in part within at leastone processing platform that implements at least a portion of the hostdevice 102.

The term “processing platform” as used herein is intended to be broadlyconstrued so as to encompass, by way of illustration and withoutlimitation, multiple sets of processing devices and associated storagesystems that are configured to communicate over one or more networks.For example, distributed implementations of the system 100 are possible,in which certain components of the system reside in one data center in afirst geographic location while other components of the system reside inone or more other data centers in one or more other geographic locationsthat are potentially remote from the first geographic location. Thus, itis possible in some implementations of the system 100 for the hostdevice 102 and storage system 105 to reside in different data centers.Numerous other distributed implementations of one or both of the hostdevice 102 and the storage system 105 are possible. Accordingly, thestorage system 105 can also be implemented in a distributed manneracross multiple data centers.

Additional examples of processing platforms utilized to implement hostdevices and/or storage systems in illustrative embodiments will bedescribed in more detail below in conjunction with FIGS. 8-10.

It is to be appreciated that these and other features of illustrativeembodiments are presented by way of example only, and should not beconstrued as limiting in any way.

Accordingly, different numbers, types and arrangements of systemcomponents such as host device 102, network 104, storage system 105,disk array enclosure 106, storage controller 108, cache 109, datastorage devices 110, metadata storage devices 112, enclosure controllers114, network devices 116, memory 118, cache 120 and connections 126 canbe used in other embodiments.

It should be understood that the particular sets of modules and othercomponents implemented in the system 100 as illustrated in FIG. 1 arepresented by way of example only. In other embodiments, only subsets ofthese components, or additional or alternative sets of components, maybe used, and such components may exhibit alternative functionality andconfigurations. Additional examples of systems implementingfunctionality for offloading using the enclosure controllers 114 will bedescribed below.

Data striping in some embodiments may be implemented on the data storagedevices 110 of the disk array enclosure 106 according to a RAIDarrangement. In such embodiments, for example, the number of datastorage devices in the RAID arrangement may comprise a prime number k,and a column of the RAID arrangement comprises k−1 blocks. In someembodiments, the data storage devices 110 may implement RAID 6 with thenumber of data storage devices being k and the number of parity datastorage devices being n, where n is greater than one (e.g., where n=2).In some embodiments, the stripe column size is selected as a multiple ofa designated block size. The multiple may be a prime number P minus 1.The prime number P may be the same as or different than the primenumbers selected for different ones of the stripes.

In some cases, the prime number selected for a particular stripe may begreater than a number of the data storage devices in the storage systemthat store data blocks for that stripe. To handle such situations, theparity blocks for the stripe may be computed by assuming or setting aset of virtual data storage devices with pages storing designatedpredetermined values (e.g., zero pages). The particular number ofvirtual data storage devices in the set may be equal to the differencebetween the prime number selected for that stripe and the number of datastorage devices in the disk array enclosure which store data blocks forthat stripe.

The term RAID, as used herein, is an umbrella term for computer datastorage schemes that can divide and replicate data among multiplephysical data storage devices, in some embodiments referred to also asdisk drives. The terms storage devices, disks and drives will be usedinterchangeably henceforth. The physical disks are said to be in a RAIDarray, which is accessed by an operating system as one single disk. Thedifferent schemes or architectures are named by the word RAID followedby a number (e.g., RAID 0, RAID 1, etc.). Each scheme provides adifferent balance between the goals of increasing data reliability andincreasing input/output performance. While in some embodiments, thestorage system is described herein with reference to a RAID array havinga RAID 6 scheme, any other RAID scheme may be used in the disclosedembodiments.

The RAID 6 scheme was developed to provide functionality for recoveringfrom a multiple disk failure (e.g., similar to RAID 1.3) with highutilization rates (e.g., comparable to RAID 4 and 5) that avoids systembottlenecks. RAID 6 uses an N+2 parity scheme, which allows failure oftwo disks, where N is the number of disks in the array. RAID 6 definesblock-level striping with double distributed parity and provides faulttolerance of two drive failures, so that the array continues to operatewith up to two failed drives, irrespective of which two drives fail.

There are various implementations of RAID 6, which may use varyingcoding schemes. As the term is used herein, RAID 6 is defined as any N+2coding scheme which tolerates double disk failure, while user data iskept in the clear. This additional requirement assures that user readsare not affected by the RAID scheme under normal system operation.Examples of RAID 6 schemes include those that utilize the Reed Solomonerror correction code and those that utilize parity bits, such as thosewherein N data disks are supported by two redundancy disks each holdinga different parity bit. It should be noted that if all parity bits areon the same two disks, then the performance may be subject tobottlenecks. This can be solved by use of distributed parity stripesover N+2 disks similar to that specified in RAID 5. Examples of codingschemes based on parity calculations of rows and diagonals in a matrixof blocks include Even/Odd and Row Diagonal Parity (RDP). Both of theseschemes utilize a first parity disk “P” that holds the parityinformation of rows of blocks as well as a second parity disk “Q” thatcontains blocks that hold the parity information of diagonals of datablocks. In both schemes, it is advantageous to work with a block sizethat is smaller than the native page size. For example, the native pagesize may be 8 kilobytes (KB), while the block size is smaller but evenlydivisible into 8 KB, e.g., 0.5 KB, 1 KB, 2 KB, 4 KB. In an example wherethe native page size is 8 KB and the block size is 2 KB, each stripethus may contain four rows, and thus the four blocks present on eachdisk form a single native page. However, a stripe can also be defined bymultiple rows of blocks distributed across the storage devices of theRAID array. It is assumed that pages are read and written using a singledisk operation.

It should be appreciated that there are various other ways to distributedata blocks in an array such as the example RAID array. For example, insome cases it may be desired to provide more than one row parity column,which results in higher capacity overhead but which allows for a fasterrebuild after a single disk failure.

Additional details regarding the above-described techniques for storingdata in RAID arrays are disclosed in U.S. Pat. No. 9,552,258, entitled“Method and System for Storing Data in RAID Memory Devices,” which isincorporated by reference herein.

FIG. 3 illustrates a representation of an example implementation of aRAID arrangement in the disk array enclosure 106 of FIGS. 1 and 2. TheRAID arrangement comprises stripe ranges 302-1, 302-2 . . . 302-N eachcomprising a plurality of stripes 304-1, 304-2, 304-3, 304-4, 304-5,304-6 . . . 304-P. The stripes 304 are each divided amongst the DSDs110-1, 110-2, 110-3 . . . 110-S-1, 110-S. Each stripe 304-1, 304-2,304-3, 304-4, 304-5, 304-6 . . . 304-P has a corresponding stripemetadata page 306-1, 306-2, 306-3, 306-4, 306-5, 306-6 . . . 306-P whichis stored in the metadata storage devices 112. Each stripe range 302-1,302-2 . . . 302-N also has a corresponding stripe range metadata page308 stored in the metadata storage devices 112. The stripe rangemetadata pages 308 may be based at least in part on the stripe metadatapages 306.

Each stripe range 302 also has a corresponding dirtyQ data structure310, also referred to as dirtyQ DS 310 in FIG. 3. DirtyQ data structure310 is a data structure stored in memory 118 of the disk array enclosure106, e.g., in one or both of memory 118-1 and 118-2 in the example diskarray enclosure 106 of FIG. 2, and is utilized in conjunction withdestage operations to quickly find all data pages for the correspondingstripe range 302. In some embodiments, a single dirtyQ data structure310 may be stored in the memory 118 and divided into portions associatedwith each stripe range 302. Each entry in the dirtyQ data structure 310comprises an indication of an offset into a stripe 304 and is removedafter the entire stripe 304 is hardened, e.g., to the data storagedevices 110. In the event of corruption, loss of power, or any otherissue that impacts the content of the dirtyQ data structure 310, thedirtyQ data structure 310 may be reconstructed from the stripe metadatapages 306, e.g., by scanning through the stripe metadata pages 306.

Modern storage systems leverage flash drives to provide fast reliablede-duplicated compressible in-place-update storage. One of thechallenges in such storage systems is lack of true scaling capabilitieswhere computational power and storage capacity are completelyindependent. For example, many existing systems have a building blockwhich is called a brick that comprises a set number of storagecontrollers and a set number of capacity entities such as disk arrayenclosures. Because the storage controllers and capacity entities aretied together, the computing power and storage capacity of such astorage system cannot be independently scaled. For example, a desire toadd computing power will result in the addition of capacity even wheresuch capacity is not needed. Likewise, a desire to add capacity willalso result in the addition of computing power even where such computingpower is not needed.

The disclosed techniques implemented by offload logic 122 of the diskarray enclosure 106 provide a scalable and standalone capacity entitywith deduplication capabilities, data protection, e.g., RAID, andindependent metadata handling with a well-defined key-value storeapplication programming interface (API). For example, the disclosedtechniques and disk array enclosure 106 provide complete de-coupling ofthe storage controller 108, also called a compute node, from the diskarray enclosure 106, also called a storage node, which allows forindependent scaling of either computing power or capacity.

The offload logic 122 is configured to implement a number of APIoperations including, for example, a write operation, a read operation,an increment operation, a decrement operation and a fused operation.These operations may be submitted to the offload logic 122 by thestorage controller 108 or from the host device 102.

The write operation comprises data to be written to the data storagedevices 110 of the disk array enclosure 106. For example, the writeoperation may comprise a fixed data block of 8K. The enclosurecontroller 114 will store the data on the data storage devices andreturn a logical identifier as a response once the data is securelystored and RAID protected on the data storage devices 110. As anexample, the logical identifier may comprise a 20B hash key. In someembodiments, the 20B hash key is derived by the enclosure controller 114from a content of the data. For example, the 20B hash key may comprise acontent-based signature generated based on the data. As part of thewrite operation, offload logic 122 may also compress the data accordingto one or more RAID operations prior to storage on the data storagedevices 110. The enclosure controller 114 may also generate or updatemetadata in the metadata storage devices 112 corresponding to thelogical identifier and the location of the data on the data storagedevices 110.

The read operation comprises a logical identifier, e.g., the 20B hashkey. The enclosure controller 114 will obtain the data from the datastorage devices 110 based at least in part on the logical identifier.For example, the logical identifier may be utilized by the enclosurecontroller 114 to identify a corresponding metadata page in the metadatastorage devices 112 and the location of the data on the data storagedevices 110 may be determined based on the metadata page. The enclosurecontroller 114 may obtain the data from the determined location andreturn the data, e.g., the 8K data block, as a response to the readoperation. Should there be a failure on one or more of the data storagedevices 110, enclosure controller 114 may perform one or more RAIDoperations to restore any missing data. In some embodiments, theenclosure controller 114 may also decompress the data before returningit as a response to the read operation, if necessary.

The increment operation comprises the logical identifier. The enclosurecontroller 114 increases a reference count in the metadata associatedwith the data block corresponding to the logical identifier that isstored on the metadata storage devices 112.

The decrement operation comprises the logical identifier. The enclosurecontroller 114 decreases a reference count in the metadata associatedwith the data block corresponding to the logical identifier that isstored on the metadata storage devices 112. In the event that thedecrement decreases the reference count to a threshold value, e.g., 0,the enclosure controller 114 may designate the data block to be freed upas part of a garbage collection process.

The fused operation comprises a combination of two or more operations.For example, the fused operation may comprise a combination of severalof the above operations, e.g., two or more write operations, readoperations, increment operations, decrement operations, or anycombination thereof. If one or more of the operations included in thefused operation fails, the enclosure controller 114 is configured toreturn a failure as a response to the fused operation.

The enclosure controller 114 is configured to mirror the metadata, e.g.,stripe metadata pages 306 and stripe range metadata pages 308,associated with the data stored on the data storage devices 110 on themetadata storage devices 112 in order to protect the integrity of themetadata. The metadata stored on the metadata storage devices 112 alsocomprises mappings of the physical locations of the data on the datastorage devices 110 to the logical identifier corresponding to thatdata, e.g., the content-based signature. In some embodiments, eachstripe metadata page 306 comprises 4K bytes and represents an entireRAID stripe 304. Each time data needs to be written to or read from thedata storage devices 110, or the reference count corresponding to thepage needs to be incremented or decremented, the corresponding stripemetadata page is read by the enclosure controller 114 into memory 118.The stripe metadata page 306 is used by the enclosure controller 114 todetermine the physical location of the data on the data storage devices110. Once the physical location has been determined, the enclosurecontroller may obtain the data from the physical location.

In some embodiments, for example, the capacity of the data storagedevices 110 is divided into equal size stripe ranges 302, e.g., at least256 stripe ranges. Each stripe range 302 has a corresponding striperange metadata page 308 and is divided into equal size stripes 304,e.g., 64K stripes in a given stripe range 302. Each stripe 304 also hasa corresponding stripe metadata page 306. In illustrative embodiments,each stripe 304 is filled with data blocks having different sizes aftercompression by the enclosure controller 114.

Illustrative embodiments of the techniques and functionality of offloadlogic 122 will now be described in more detail with reference to FIGS. 4and 5. The processes of FIGS. 4 and 5 are described with reference alsoto FIGS. 1-3.

The process as shown in FIG. 4 includes steps 400 through 410, and issuitable for use in the system 100 but is more generally applicable toother types of systems comprising multiple host devices and a sharedstorage system. The process of FIG. 4 occurs when a write operation isreceived by the enclosure controller 114 from a storage controller 108or host device 102.

At step 400, the offload logic 122 of enclosure controller 114 receivesa write operation from the storage controller 108 or the host device102. For example, storage controller 108 may obtain an IO writeoperation from the host device, log the IO write operation in a writecache and then destage the write cache to the enclosure controller 114for hardening to the data storage devices 110. The received writeoperation comprises data to be written to at least one of the datastorage devices 110. For example, the write operation may comprise an 8Kblock of data to be written to at least one of the data storage devices.

At step 402, offload logic 122 determines a logical identifier for thedata based at least in part on the received write operation. Forexample, a hashing algorithm may be performed on the content of the datato determine a 20B hash value as the logical identifier, e.g., acontent-based signature. In some embodiments, the data may be compressedbefore or after determining the logical identifier.

At step 404, offload logic 122 determines a physical location on atleast one of the data storage devices 110 for storing the given data.For example, the determined physical location may comprise the nextavailable physical location in at least one of the data storage devices110.

At step 406, offload logic 122 stores the data on the data storagedevices 110 at the determined physical location.

At step 408, offload logic 122 updates the metadata stored on the atleast one metadata storage device based at least in part on thedetermined physical location and the determined logical identifier. Forexample, offload logic 122 may access the metadata stored in themetadata storage devices 112 to update a mapping between the determinedlogical identifier and the corresponding physical location. In someembodiments, for example, offload logic 122 may identify a stripe rangemetadata page 308 based at least in part on the determined logicalidentifier. Offload logic 122 may then identify a stripe metadata page306 based at least in part on the determined logical identifier and theidentified stripe range metadata page 308. For example, the stripemetadata page 306 may correspond to an offset into the stripe rangemetadata page 308. The offset may correspond to a stripe index, e.g.,derived from the logical identifier, multiplied by a metadata page size,e.g., 4 KB. Offload logic 122 may then search the identified stripemetadata page for an entry comprising the determined logical identifierand update the entry in the identified stripe metadata page by mappingthe determined logical identifier to the determined physical location inthe entry. In some embodiments, if no entry comprising the determinedlogical identifier is present, a new entry comprising the mappingbetween the determined logical identifier and the determined physicaladdress may be added to the stripe metadata page.

At step 410, the logical identifier is returned as a response to thewrite operation.

The process as shown in FIG. 5 includes steps 500 through 510, and issuitable for use in the system 100 but is more generally applicable toother types of systems comprising multiple host devices and a sharedstorage system. The process of FIG. 5 occurs when a read operation isreceived by the enclosure controller 114 from a storage controller 108or host device 102.

At step 500, the offload logic 122 of the enclosure controller 114receives a read operation comprising a logical identifier correspondingto data stored on the data storage devices 110.

At step 502, offload logic 122 identifies, based at least in part on thelogical identifier, a corresponding stripe range metadata page 308stored in the metadata storage device 112. For example, a portion of thelogical identifier may correspond to the stripe range metadata page 308.

At step 504, offload logic 122 identifies, based at least in part on thelogical identifier and the identified stripe range metadata page 308, acorresponding stripe metadata page 306 stored in the metadata storagedevice 112. For example, a portion of the logical identifier maycorrespond to the stripe metadata page 306.

At step 506, offload logic 122 determines the physical location of thedata on at least one of the data storage devices 110 based at least inpart on the identified stripe metadata page 306. For example, theoffload logic 122 may search the identified stripe metadata page 306 foran entry comprising the logical identifier and determine the mappingbetween the logical identifier and the physical location based at leastin part on that entry. If an entry comprising the logical identifier isnot included in the stripe metadata page 306, offload logic 122 mayreturn an error or other failure indicating that the data is notavailable.

At step 508, offload logic 122 obtains the data from the determinedphysical location.

At step 510, offload logic 122 returns the obtained data as a responseto the received read operation.

The use of offload logic 122 to implement RAID and mapping operationswithin the disk array enclosure 106 instead of on the storage controller108, as described above, saves a significant amount of bandwidth andprocessing power as compared to approaches where the RAID operations andmapping are performed entirely or partially by the storage controller108. In illustrative embodiments, the storage controller 108 need onlyprovide the disk array enclosure 106 with the data to be stored, in thecase of a write operation, or the logical identifier corresponding tothe data, in the case of a read operation, increment operation ordecrement operation. The enclosure controller 114 will then handle allRAID processing such as, e.g., write flow, compression and errorhandling, and logical identifier to physical location mapping. Inaddition, by including this functionality within the disk arrayenclosure 106, the disk array enclosure 106 and the storage controller108 may be more easily separated for scaling of the compute power orcapacity of the storage system without requiring a similar scaling ofthe other.

Referring again to FIG. 2, in some embodiments, example disk arrayenclosure 106 comprises three metadata storage devices 112. While onlythree metadata storage devices 112 are illustrated, example disk arrayenclosure 106 may comprise any other number of metadata storage devices112.

In illustrative embodiments, the metadata storage devices 112 aremirrored with the same metadata to provide redundancy. For example, eachmetadata storage device 112 will have a complete copy, i.e., a mirror,of all of the metadata for the example disk array enclosure 106 in orderto provide improved performance, throughput, availability andcontinuity.

For example, by providing multiple mirrored metadata storage devices 112in the illustrative embodiments, performance may be improved since eachmetadata storage device 112 can handle a portion of the incoming read,write or other operations in parallel with the other metadata storagedevices 112. For example, if each metadata storage device 112 is capableof servicing 500 KIops worth of read, write or other operations, usingall three metadata storage devices 112 at the same time in parallelprovides a throughput of 1.5 MIops for the same set of metadata.

In addition, by utilizing multiple metadata storage devices 112, a highlevel of metadata availability is provided to the disk array enclosuresince even if one or more of the metadata storage devices 112 fails orotherwise has its capacity reduced, the other metadata storage devices112 are still functioning. Should some or all of the metadata storagedevices 112 fail at the same time, the metadata may be recovered from ahardened version of the metadata which is stored on the data storagedevices 110.

However, a typical three-way mirroring of the metadata storage devices112 and backup hardening to the data storage devices 110, on its own,may not provide sufficient continuity for recovering from a failure orother issue in all of the metadata storage devices 112 since themetadata associated with pending write and read operations may be lost.

In another case, one or more of the metadata storage devices 112 mayoccasionally experience a “hiccup,” e.g., a scenario where an operationthat is submitted to the metadata storage device 112 does not receive areply for a threshold amount of time. The threshold amount of time afterwhich a submitted operation times out may be defined by the applicationissuing IO operations from a host device 102, by the operating system ofthe host device 102 issuing the IO operations, by the HBA drivers orhardware of the host device 102 that are submitting the IO operations,by any component of the storage system 105 or by any other component ofthe system 100.

When a simple mirroring technique is utilized on the metadata storagedevices 112, a metadata page typically will not be written and thecorresponding operation cannot be served until all three metadatastorage devices 112 finish handling the operation. This situation maycause delays and inconsistent performance during the servicing of IOoperations by the disk array enclosure

In illustrative embodiments, the metadata storage devices 112 storestripe metadata pages 306 corresponding to stripes of data 304 stored onthe data storage devices 110. The stripe metadata pages 306 are writtensequentially and referred to by an index and an initial offset. A copyof each metadata page is stored on each of the metadata storage devices112 and an additional hardened copy is stored on a persistent storagedevice such as, e.g., the data storage drives 110 or another storagedevice assigned for that purpose.

The stripe metadata pages 306 may be partitioned in each metadatastorage device 112 between each of the enclosure controllers 114. Forexample, if there are two enclosure controllers 114, half of the stripemetadata pages 306 will be partitioned for servicing by each enclosurecontroller 114.

The memory 118 associated with each enclosure controller 114 maycomprise a plurality of dirty data structures 128, e.g., dirty datastructures 128-1 and 128-2 in the example of FIG. 2. For example, thememory 118 of each enclosure controller 114 may comprise a dirty datastructure 128 for each of the enclosure controllers 114 included in thedisk array enclosure 106. For example, memory 118-1 associated withenclosure controller 114-1 may comprise a pair of dirty data structures128-1, one for enclosure controller 114-1 and one for enclosurecontroller 114-2. The dirty data structures 128 are configured to storethe logical identifiers associated with failed or timed out metadatawrite or read operations.

Hiccup and failure management of the metadata storage devices 112 isglobally controlled for the entire disk array enclosure 106 since themetadata storage devices 112 are shared by both enclosure controllers114. For example, management functionality may be implemented within theoffload logic 122 of one of the enclosure controllers 114 for monitoringthe hiccup and failure status of each of the metadata storage devices112. For example, the management functionality may monitor each of themetadata storage devices 112 for failures or delayed responses.

The data path of the enclosure controller 114 implementing themanagement functionality is configured to notify the managementfunctionality about timeout instances associated with each read or writeoperation submitted to the metadata storage devices 112. For example,the data path may notify the management functionality as each read,write or other operation fails or times out for a given metadata storagedevice 112, e.g., on demand. In some embodiments, the data path may beconfigured to notify the management functionality for an aggregate ofread and write operation timeouts.

In addition, platform monitoring may also be utilized by the managementfunctionality to determine whether or not there are failures in themetadata storage device 112. For example, the platform monitoring maycomprise the use of polling functionality that acts at a slower ratethan the on-demand data path notifications. For example, the managementfunctionality may aggregate a threshold number of failure or timeoutnotifications together, e.g. 5 notifications, 5 notifications in aparticular period of time, or any other threshold number or rate ofnotifications, before determining that a particular metadata storagedevice 112 is suspicious and moving a state machine for that metadatastorage device 112 to a suspected hiccup state. In some examplescenarios, this process of monitoring for failures or timeouts,determining that a particular metadata storage device 112 is suspicious,and moving the state machine of the particular metadata storage device112 to the suspected hiccup state should take less than a thresholdamount of time, e.g., a few seconds, minutes, etc., in order not tooverflow the buffers. The management functionality is configured toinitiate a diagnostic of the suspicious metadata storage device 112 inresponse to the state machine of the metadata device being moved to thesuspected hiccup state.

In some cases, it may be valuable for the management functionality towait a threshold amount of time, e.g., a few minutes after moving theparticular metadata storage device 112 to the suspected hiccup state,prior to initiating the diagnostics in order to allow the metadatastorage device 112 to rest. For example, if the failure or timeouts aredue to congestion, allowing the metadata storage device 112 to restwhile in the suspected hiccup state may allow the congestion to clearout as new read and write operations are directed to the other metadatastorage devices 112.

The diagnostics may comprise, for example, submitting dummy read andwrite operations to the suspicious metadata storage device 112 anddetermining whether the suspicious metadata storage device 112 is stillhaving issues. For example, if the result of the diagnostics is that themetadata storage device 112 is functioning properly, the state machineof the suspicious metadata storage device 112 may be moved to active,the notifications may be reset, and a counter corresponding to thenumber of times that the metadata storage device 112 has been deemedsuspicious may be incremented to keep track of potential recurrences ofthe same issues in the future by the metadata storage device 112.

If the result of the diagnostics indicates that the disk is actually ina hiccup state, e.g., timeouts are still present, the managementfunctionality moves the state machine of the metadata storage device 112to the hiccup state. While in the hiccup state, each write to themetadata storage device 112 is handled as if it has timed out, e.g.,adding the write operation to a metadata journal, but not writing themetadata to the metadata storage device 112. In addition, any readoperations that are received for the metadata storage device 112 willbehave as if there is a metadata journal entry for that read operationand will redirect the read operation to one of the other metadatastorage devices 112.

If the result of the diagnostic indicates that the metadata storagedevice 112 has failed, an alert or notification is issued to theenclosure controllers 114 with instructions to stop using the failedmetadata storage device 112.

In some cases, as an optimization, if a threshold period of time haselapsed since the metadata storage device 112 failed and the metadatastorage device 112 has not yet been replaced, management functionalitymay attempt to revive the metadata storage device 112. For example, themanagement functionality may reset the metadata storage device 112,reformat the metadata storage device 112, power cycle the metadatastorage device 112, or perform any other management function on themetadata storage device 112 in an attempt to revive the metadata storagedevice 112 back into functional use.

The duration that the state machine of the metadata storage device 112remains in the hiccup state may be determined by the managementfunctionality, for example, based on a predefined timeout value, byquerying an internal drive API of the metadata storage device 112, ifavailable, or in any other manner. If the metadata storage device 112 isdeemed health, the state machine is moved to the active state, and themanagement functionality may issue a command to resynchronize themetadata storage device 112 with the remaining metadata storage devices112 as part of a background process.

In some cases, if a metadata storage device 112 was declared assuspicious, e.g., by incrementing the counter, more than a thresholdnumber of times, e.g., 5 times, in the past threshold amount of time,e.g., 5 minutes, the management functionality may attempt to revive themetadata storage device 112, for example, by performing a warm or coldreset of the metadata storage device 112, PCIe ports, or other hardwareand running the diagnostic again.

While the management functionality of the offload logic 122 of theenclosure controller 114 handles the timeout and failure of the metadatastorage device 112, new write, read or other operations continue to beissued for the other metadata storage devices 112. In order to managethese operations while a drive is in the suspected hiccup state or inthe hiccup state, a journaling mechanism may be utilized. For example, ametadata journal 124 which is stored in the cache 120 of the disk arrayenclosure 106 may be utilized by the enclosure controller 114 to handlewrite, read and other operations that require servicing while aparticular metadata storage device 112 is in the suspected hiccup stateor hiccup state. In some embodiments, the cache 120 may comprisepersistent memory which stores the metadata journal 124.

An example flow will now be described for when a stripe metadata page306 is being updated by the enclosure controller 114. The enclosurecontroller 114 may attempt to update a stripe metadata page 306 in anumber of different scenarios.

For example, if the storage controller 108 is destaging the cache 109,e.g., write cache, to the disk array enclosure 106 for storage on thedata storage devices 110, stripe metadata pages 306 associated with thedestaged data may need to be updated by the enclosure controller 114.

In another scenario, when the stripe metadata pages 306 themselves aredestaged for hardening in the data storages devices 110 as a backupcopy, corresponding stripe metadata pages 306 may also need to beupdated accordingly.

In yet another scenario, when a write operation includes duplicate data,e.g., the logical identifier generated based on the data matches alogical identifier in the metadata storage devices 112 which is alreadymapped to a physical location, a reference count for that data page maybe incremented in the metadata storage devices 112. Likewise, in thecase where the data that was stored on the data storage devices 110 haschanged or is no longer needed by a particular application, a referencecount associated with the data in the metadata storage devices 112 maybe decremented which requires an update to the corresponding stripemetadata page 306.

During an update of a given stripe metadata page 306, enclosurecontroller 114 may attempt to write the stripe metadata page 306 to eachof the metadata storage devices 112. If all of the metadata storagedevices 112 fail the write, an error code may be returned to the storagecontroller 108 or host device 102 by the enclosure controller 114.

In addition, for each failed write operation, the managementfunctionality may be notified, e.g., asynchronously after the responseis provided to the storage controller 108 or host device 102. Thefailure may be journaled in the metadata journal 124 by adding an entrycomprising a device identifier for the failed metadata storage device112 and a metadata identifier corresponding to the location of thestripe metadata page 306 in the metadata storage device 112. The dirtydata structures 128 of each enclosure controller 114 that correspond tothe stripe metadata page 306 of the failed metadata storage device 112,depending on how the stripe metadata pages 306 were partitioned betweenthe enclosure controllers 114, may be updated to add an entrycorresponding to the logical identifier of the failed write operation.The dirty data structure 128, metadata journal 124, or another portionof enclosure controller 114 may set an indication that a hardening ofthe stripe metadata page 306 to the failed metadata storage device 112is required in the future.

For each successful write operation, the enclosure controller 114determines whether or not an entry already exists in the metadatajournal 124 for the corresponding logical identifier. If such an entryexists, enclosure controller 114 invalidates the entry and updates thedirty data structure 128 to remove the logical identifier from the listof stripes metadata pages 306 to be hardened.

For read operations, each thread of the enclosure controller 114 willutilize a different metadata storage device 112 from which to read thestripe metadata pages 306. This allows reads to exhibit improvedperformance. Initially, the thread of the enclosure controller 114 thatis handling the read operation for a particular metadata storage device112 will query the dirty data structure 128 associated with theparticular metadata storage device 112 to determine whether or not thelogical identifier associated with the read operation, e.g., provided aspart of the read operation, is included in the dirty data structure 128associated with the particular metadata storage device 112. For example,the query may determine whether or not the particular metadata storagedevice 112 holds the latest data for this read operation. If the logicalidentifier is included in the dirty data structure 128, the enclosurecontroller 114 will instead attempt the read operation on one of theother metadata storage devices 112.

In the case that none of the metadata storage devices 112 are healthy orhave the latest data for the read operation, a copy of the correspondingstripe metadata page 306 is read from the hardened copy stored in thedata storage devices 110. In some embodiments, in the case that theparticular metadata storage device 112 was moved from the hiccup stateor suspected hiccup state to the active state and the stripe metadatapage 306 is read from the hardened copy stored in the data storagedevices 110 or from one of the other metadata storage devices 112,enclosure controller 114 may take advantage of the read of the stripemetadata page 306 and resync the stripe metadata page 306 to theparticular metadata storage device 114, e.g., by updating thecorresponding stripe metadata page 306 in the particular metadatastorage device 112.

Upon a failover of one of the enclosure controllers 114, e.g., enclosurecontroller 114-1, the neighboring enclosure controller 114, e.g.,enclosure controller 114-2 will take over responsibility for the stripemetadata pages 306 that were partitioned to that enclosure controller114-1. In the case of a dual enclosure controller configuration,enclosure controller 114-2 may take over full responsibility for allstripe metadata pages 306 of the metadata storage devices 112. As partof this responsibility, enclosure controller 114-2 is configured toreview the metadata journal 124 and reconstruct the dirty data structure128 corresponding to the failed enclosure controller 114-1. Once thefailed enclosure controller 114-1 comes back online, the reconstructeddirty data structure 128 may be cleared out.

When a failed metadata storage device 112 or a metadata storage device112 that was in the hiccup state has been moved to the active state, aresynchronization flow is initiated. For example, enclosure controller114 may trigger a resynchronization by activating a background processor thread. The background process reviews the metadata journal 124 todetermine whether any entries correspond to the metadata storage device112 that has been moved back to the active state. If any such entriesexist, the corresponding stripe metadata pages 306 are read from anothervalid version, e.g., as stored on one of the other metadata storagedevices 112, or from the hardened copy on the data storage devices 110if necessary, and written to the metadata storage device 112. Thecorresponding metadata journal entries are then invalidated since theyhave been hardened to the metadata storage device 112. In some cases,the resynchronization may also be triggered when the size or number ofentries in the metadata journal 124 reaches a threshold value. Forexample, when the size or number of entries in the metadata journal 124reaches a certain percentage of a total size or number of entries, themetadata journal 124 may be destaged by synchronizing the metadatastorage devices 112 with their corresponding journaled stripe metadatapage writes.

Illustrative embodiments of the techniques and functionality of offloadlogic 122 will now be described in more detail with reference to FIG. 6.The process of FIG. 6 is described with reference also to FIGS. 1-3.

The process as shown in FIG. 6 includes steps 600 through 606, and issuitable for use in the system 100 but is more generally applicable toother types of systems comprising multiple host devices and a sharedstorage system. The process of FIG. 6 occurs when a write operation isreceived by the enclosure controller 114 from a storage controller 108or host device 102.

At step 600, the offload logic 122 of enclosure controller 114 writes astripe metadata page 306 to the metadata storage devices 112.

At step 602, the offload logic 122 determines that the write failed forone or more of the metadata storage devices 112. For example, the writemay fail for metadata storage device 112-1 but succeed for metadatastorage devices 112-2 and 112-3.

At step 604, the offload logic 122 adds an entry to the metadata journal124 based at least in part on the determination that the write to one ormore of the metadata storage devices 112, e.g., metadata storage device112-1, has failed. As mentioned above the entry may comprise a deviceidentifier which identifies the metadata storage device 112 that failed,e.g., metadata storage device 112-1, and a metadata identifier thatidentifies the particular stripe metadata page that failed to bewritten.

At step 606, the offload logic sets an indication in a data structureassociated with the disk array enclosure 106 that the stripe metadatapage 306 has not been written to the metadata storage device 112 thatfailed, e.g., metadata storage device 112-1, and therefore has not beenhardened to the metadata storage device 112 that failed, the datastorage devices 110, or both. In some cases, the indication may be setas part of the metadata journal 124. In some cases, the indication maybe set as part of the dirty data structure 128 or any other datastructure of the disk array enclosure 106.

In some embodiments, the amount of available memory 118 on the diskarray enclosure 106 for use by the enclosure controllers 114 is unableto hold all of the stripe metadata pages 306 stored on the metadatastorage devices 112. For example, in order to reduce the cost of theprocessing and memory components of the disk array enclosure 106,components with reduced capabilities may be utilized. This provides somechallenges when attempting to efficiently access and utilize themetadata stored in the metadata storage devices 112.

In illustrative embodiments, offload logic 122 implements functionalityfor improving the speed at which stripe metadata pages 306 are obtainedfrom the metadata storage devices 112.

In a typical read flow, an enclosure controller 114 may receive a readoperation from the storage controller 108 or host device 102. The readoperation typically comprises a logical identifier such as, e.g., a hashkey or content-based signature, that was previously generated by one ofthe enclosure controllers 114 and provided to the storage controller 108or host device 102 as a response to a write operation. The enclosurecontroller 114 then determines a metadata identifier, e.g., stripeindex, based at least in part on the logical identifier. For example, aportion of the logical identifier may be utilized by the enclosurecontroller 114 to identify a corresponding stripe range metadata page308. A portion of the logical identifier in conjunction with the striperange metadata page 308 may then be utilized to determine thecorresponding metadata identifier.

The metadata identifier, e.g., stripe index, is then used to determinethe offset to the corresponding stripe metadata page 306. The stripemetadata page 306 is searched to locate an entry corresponding to thelogical identifier. If no entry corresponding to the logical identifieris found, the enclosure controller 114 returns an indication of afailure, e.g., a hash not found response. If an entry corresponding tothe logical identifier is found in the stripe metadata page 306,enclosure controller 114 utilizes the entry to obtain the mapping of thelogical identifier to the corresponding physical location on the datastorage devices 110. The enclosure controller 114 reads the data fromthe obtained physical location. In a case where the data is compressed,enclosure controller 114 performs one or more RAID operations on thedata to decompress the data. If the read or decompression fails, theenclosure controller 114 goes into degraded mode and reclaims the lostdata using one or more RAID error recovery processes. If the read ordecompression is successful, and enclosure controller 114 obtains thedata page corresponding to the read operation, validates the data page,and provides the data page to the storage controller 108 or host device102 in response to the read operation. In some cases, an RDMA write ofthe data page to a pre-allocated buff may be utilize for transferringthe data page to the storage controller 108 or host device 102 in orderto improve performance.

Determining the metadata identifier, e.g., the stripe index, may be acostly and time-consuming process. For example, one approach comprisesobtaining the metadata for each stripe 304 in a stripe range 302, e.g.,64 K stripes each having 64 K pages of metadata. For each stripemetadata page 306, each entry is compared to the logical identifier,e.g., 480 entry comparisons. Such a method of determining the stripeindex may be very costly in terms of processing power and latency. Forexample, if the reading and processing of a single stripe metadata pagetakes roughly 30 μs, the entire search of all of the 64K stripe indicesin the stripe range may take about 2 seconds.

Since reading 64K pages of metadata takes too long, a data structure maybe employed that will help reduce number of metadata pages to a numberof hashes in a hash bucket, e.g., approximately 100 hashes instead of64K metadata pages. For example, a hash bucket-based data structure maybe utilized where each hash bucket may comprise all stripe indices in agiven stripe range that contain entries, e.g., logical identifiers. Inthis manner, only those stripe indices which contain entries need beexamined in more detail and the remaining process may be the same asabove where, for example, the pages of metadata corresponding to thestripe indices in the bucket will be examined and the correspondingentries compared to the logical identifier. Once the logical identifieris found in one of the stripe metadata pages the mapping to the physicallocation of the corresponding data may be determined.

In illustrative embodiments, the speed of the search for a given logicalidentifier in the metadata may be improved through the use of a metadataidentifier. In some embodiments, the metadata identifier comprises ahint such as, e.g., the stripe index. In response to a write operation,enclosure controller 114 may be configured to return not only anindication of a successful write, e.g., the logical identifier itself,but also the metadata identifier. For example, the storage controller108 or host device 102 may receive both the logical identifier and themetadata identifier in response to the submission of a write operationto the enclosure controller 114.

In addition, when a future read operation is submitted to the enclosurecontroller 114, the read operation may comprise both the logicalidentifier and the metadata identifier which facilitates fasterprocessing of the read operation.

In illustrative embodiments, enclosure controller 114 comprises an APIfor servicing read and write operations. For example, the API mayfunction as follows when an operation is received from the storagecontroller 108 or host device 102.

As an example, when a write operation is received by enclosurecontroller 114, enclosure controller 114 may perform some or all of theprocessing described above and then return the logical identifier andthe metadata identifier as outputs.

As another example, when a read operation, increment operation ordecrement operation is received by enclosure controller 114 thatcomprises both a logical identifier for the target data page and themetadata identifier, the logical identifier and the metadata identifiermay be utilized to locate the metadata page without the searchingdescribed above and only the comparison of the logical identifier to theentries in that metadata page need be performed for determining themapping of the logical identifier to the physical location of the targetdata. The fused operation may also or alternatively be received. In someembodiments, if the metadata identifier is not included in theoperation, the full flow described above may alternatively be utilizedto determine the mapping.

An example flow using metadata identifiers will now be described.Initially, enclosure controller 114 obtains a read operation. The readoperation comprises both the logical identifier and the metadataidentifier. The enclosure controller 114 obtains a stripe index based atleast in part on the metadata identifier and obtains the correspondingstripe metadata page, e.g., a 4 KB metadata page. For example, an offsetfor the stripe metadata page may comprise the stripe index multiplied bythe size of the stripe metadata pages. The logical identifier may thenbe compared to the entries in the obtained stripe metadata page todetermine the mapping between the logical identifier and the physicallocation of the data on the data storage devices. The remainder of theprocess may occur as described above including decompressing the pagedata if needed, recovering the page data if needed, validating the pagedata, and returning a response comprising the page data. In someembodiments, a RDMA write of the page to a pre-allocated buffer may beutilized to improve performance.

By including the metadata identifiers, e.g., stripe indexes, as part ofread, increment, and decrement operations, or returning the metadataidentifier as part of the write operation, the read, increment anddecrement operations may quickly and efficiently obtain the stripemetadata page comprising an entry corresponding to the logicalidentifier.

Illustrative embodiments of the techniques and functionality of offloadlogic 122 will now be described in more detail with reference to FIG. 7.The process of FIG. 7 is described with reference also to FIGS. 1-3.

The process as shown in FIG. 7 includes steps 700 through 708, and issuitable for use in the system 100 but is more generally applicable toother types of systems comprising multiple host devices and a sharedstorage system. The process of FIG. 7 occurs when a write operation isreceived by the enclosure controller 114 from a storage controller 108or host device 102.

At step 700, enclosure controller 114 receives a write operationcomprising data to be stored on at least one of the plurality of datastorage devices.

At step 702, enclosure controller 114 determines a logical identifierfor the data based at least in part on the received write operation.

At step 704, enclosure controller 114 determines a metadata identifiercorresponding to a metadata page on the at least one metadata storagedevice that is associated with the logical identifier.

At step 706, enclosure controller 114 updates the metadata page based atleast in part on the metadata identifier.

At step 708, enclosure controller 114 returns the logical identifier andthe metadata identifier as a response to the received write operation.

It is to be understood that the ordering of the process steps of theprocesses of FIGS. 4-7 may be varied in other embodiments, or certainsteps may be performed at least in part concurrently with one anotherrather than serially. Also, one or more of the process steps may berepeated periodically, or multiple instances of the process can beperformed in parallel with one another in order to implement a pluralityof different processes for different storage systems or for differentRAID arrays or other data striping schemes on a particular storagesystem or systems.

Functionality such as that described herein can be implemented at leastin part in the form of one or more software programs stored in memoryand executed by a processor of a processing device such as a computer orserver. As will be described below, a memory or other storage devicehaving executable program code of one or more software programs embodiedtherein is an example of what is more generally referred to herein as a“processor-readable storage medium.”

For example, an enclosure controller such as enclosure controller 114that is configured to control performance of one or more steps of theprocesses of FIGS. 4-7 described herein can be implemented as part ofwhat is more generally referred to herein as a processing platformcomprising one or more processing devices each comprising a processorcoupled to a memory. Such processing devices are to be distinguishedfrom processing devices referred to herein with respect to theprocessing capabilities of the SSDs. In the case of a host device orstorage controller, a given such processing device may correspond to oneor more virtual machines or other types of virtualization infrastructuresuch as Docker containers or Linux containers (LXCs). The host device102 of system 100, as well as other system components, may beimplemented at least in part using processing devices of such processingplatforms. For example, in a distributed implementation of the storagecontroller 108, respective distributed modules of such a storagecontroller can be implemented in respective containers running onrespective ones of the processing devices of a processing platform.

In some embodiments, the storage system comprises an XtremIO™ storagearray or other type of content addressable storage system suitablymodified to incorporate functionality for offloading as disclosedherein.

An illustrative embodiment of such a content addressable storage systemwill now be described with reference to FIG. 8. In this embodiment, acontent addressable storage system 805 comprises one or more computenodes 815 and one or more capacity nodes 817.

Compute nodes 815 comprise storage controllers 808 and cache 809.

Capacity nodes 817 comprise data storage devices 810, metadata storagedevices 812, enclosure controllers 814, network devices 816, memory 818,and cache 820 which are similar to data storage devices 110, metadatastorage devices 112, enclosure controllers 114, network devices 116,memory 118 and cache 120, as described above.

The content addressable storage system 805 may be viewed as a particularimplementation of the storage system 105, and accordingly is assumed tobe coupled to host devices 102 of computer system 101 via network 104within information processing system 100.

The enclosure controller 814 in the present embodiment is configured toimplement offloading functionality of the type previously described inconjunction with FIGS. 1 through 7.

The enclosure controller 814 includes offload logic 822, which isconfigured to operate in a manner similar to that described above forrespective corresponding offload logic 122.

The cache 809 is configured to operate in a manner similar to thatdescribed above for cache 109.

The content addressable storage system 805 in the FIG. 8 embodiment isimplemented as at least a portion of a clustered storage system andincludes a plurality of compute nodes 815 each comprising acorresponding subset of the storage devices 806. Other clustered storagesystem arrangements comprising multiple compute nodes can be used inother embodiments. A given clustered storage system may include not onlycompute nodes 815 but also additional compute nodes coupled via astorage network. Alternatively, such additional compute nodes may bepart of another clustered storage system of the system 100. Each of thecompute nodes 815 of the storage system 805 is assumed to be implementedusing at least one processing device comprising a processor coupled to amemory.

The storage controller 808 of the content addressable storage system 805is implemented in a distributed manner so as to comprise a plurality ofdistributed storage controller components implemented on respective onesof the compute nodes 815. The storage controller 808 is therefore anexample of what is more generally referred to herein as a “distributedstorage controller.” In subsequent description herein, the storagecontroller 808 may be more particularly referred to as a distributedstorage controller.

Each of the compute nodes 815 in this embodiment further comprises a setof processing modules configured to communicate over one or morenetworks with corresponding sets of processing modules on other ones ofthe compute nodes 815. The sets of processing modules of the computenodes 815 collectively comprise at least a portion of the distributedstorage controller 808 of the content addressable storage system 805.

The modules of the distributed storage controller 808 in the presentembodiment more particularly comprise different sets of processingmodules implemented on each of the compute nodes 815. The set ofprocessing modules of each of the compute nodes 815 comprises at least acontrol module 808C, a data module 808D and a routing module 808R. Thedistributed storage controller 808 further comprises one or moremanagement (“MGMT”) modules 808M. For example, only a single one of thecompute nodes 815 may include a management module 808M. It is alsopossible that management modules 808M may be implemented on each of atleast a subset of the compute nodes 815.

Each of the compute nodes 815 of the storage system 805 thereforecomprises a set of processing modules configured to communicate over oneor more networks with corresponding sets of processing modules on otherones of the compute nodes. A given such set of processing modulesimplemented on a particular storage node illustratively includes atleast one control module 808C, at least one data module 808D and atleast one routing module 808R, and possibly a management module 808M.These sets of processing modules of the compute nodes collectivelycomprise at least a portion of the distributed storage controller 808.

Communication links may be established between the various processingmodules of the distributed storage controller 808 using well-knowncommunication protocols such as IP, Transmission Control Protocol (TCP),and remote direct memory access (RDMA). For example, respective sets ofIP links used in data transfer and corresponding messaging could beassociated with respective different ones of the routing modules 808R.

The metadata storage devices 812 are configured to store metadata pages824 and the data storage devices 810 are configured to store user datapages 826 and may also store additional information not explicitly shownsuch as checkpoints and write journals. The metadata pages 824 and theuser data pages 826 are illustratively stored in respective designatedmetadata and user data areas of the metadata storage devices 812 anddata storage devices 110. Accordingly, metadata pages 824 and user datapages 826 may be viewed as corresponding to respective designatedmetadata and user data areas of the metadata storage devices 812 anddata storage devices 810.

A given “page” as the term is broadly used herein should not be viewedas being limited to any particular range of fixed sizes. In someembodiments, a page size of 8 KB is used, but this is by way of exampleonly and can be varied in other embodiments. For example, page sizes of4 KB, 16 KB or other values can be used. Accordingly, illustrativeembodiments can utilize any of a wide variety of alternative pagingarrangements for organizing the metadata pages 824 and the user datapages 826.

The user data pages 826 are part of a plurality of logical units (LUNs)configured to store files, blocks, objects or other arrangements ofdata, each also generally referred to herein as a “data item,” on behalfof users associated with host devices 102. Each such LUN may compriseparticular ones of the above-noted pages of the user data area. The userdata stored in the user data pages 826 can include any type of user datathat may be utilized in the system 100. The term “user data” herein istherefore also intended to be broadly construed.

The content addressable storage system 805 in the embodiment of FIG. 8is configured to generate hash metadata providing a mapping betweencontent-based digests of respective ones of the user data pages 826 andcorresponding physical locations of those pages in the user data area.Content-based digests generated using hash functions are also referredto herein as “hash digests.” The hash metadata generated by the contentaddressable storage system 805 is illustratively stored as metadatapages 824 in the metadata area. The generation and storage of the hashmetadata is assumed to be performed under the control of the enclosurecontroller 814.

Each of the metadata pages 824 characterizes a plurality of the userdata pages 826. For example, a given set of user data pages representinga portion of the user data pages 826 illustratively comprises aplurality of user data pages denoted User Data Page 1, User Data Page 2,. . . User Data Page n. It should be noted that usage of the variable nin this user data page context is unrelated to its usage elsewhereherein.

Each of the user data pages 826 in this example is characterized by aLUN identifier, an offset and a content-based signature. Thecontent-based signature is generated as a hash function of content ofthe corresponding user data page. Illustrative hash functions that maybe used to generate the content-based signature include the above-notedSHA1 hash function, or other secure hashing algorithms known to thoseskilled in the art. The content-based signature is utilized to determinethe location of the corresponding user data page within the user dataarea of the storage devices 810.

Each of the metadata pages 824 in the present embodiment is assumed tohave a signature that is not content-based. For example, the metadatapage signatures may be generated using hash functions or other signaturegeneration algorithms that do not utilize content of the metadata pagesas input to the signature generation algorithm. Also, each of themetadata pages is assumed to characterize a different set of the userdata pages.

A given set of metadata pages representing a portion of the metadatapages 824 in an illustrative embodiment comprises metadata pages denotedMetadata Page 1, Metadata Page 2, . . . Metadata Page m, havingrespective signatures denoted Signature 1, Signature 2, . . . Signaturem. Each such metadata page characterizes a different set of n user datapages. For example, the characterizing information in each metadata pagecan include the LUN identifiers, offsets and content-based signaturesfor each of the n user data pages that are characterized by thatmetadata page. It is to be appreciated, however, that the user data andmetadata page configurations described above are examples only, andnumerous alternative user data and metadata page configurations can beused in other embodiments.

Ownership of a user data logical address space within the contentaddressable storage system 805 is illustratively distributed among thecontrol modules 808C.

The management module 808M of the storage controller 808 may includelogic that engages corresponding logic instances in all of the controlmodules 808C and routing modules 808R in order to implement processesassociated with the offloading functionality.

In some embodiments, the content addressable storage system 805comprises an XtremIO™ storage array suitably modified to incorporatetechniques for write flow offloading, compression offloading and erroroffloading, as disclosed herein.

In arrangements of this type, the control modules 808C, data modules808D and routing modules 808R of the distributed storage controller 808illustratively comprise respective C-modules, D-modules and R-modules ofthe XtremIO™ storage array. The one or more management modules 808M ofthe distributed storage controller 808 in such arrangementsillustratively comprise a system-wide management module (“SYM module”)of the XtremIO™ storage array, although other types and arrangements ofsystem-wide management modules can be used in other embodiments.

In the above-described XtremIO™ storage array example, each user datapage has a fixed size such as 8 KB and its content-based signature is a20-byte signature generated using an SHA1 hash function. Also, each pagehas a LUN identifier and an offset, and so is characterized by <lun_id,offset, signature>.

The content-based signature in the present example comprises acontent-based digest of the corresponding data page. Such acontent-based digest is more particularly referred to as a “hash digest”of the corresponding data page, as the content-based signature isillustratively generated by applying a hash function such as SHA1 to thecontent of that data page. The full hash digest of a given data page isgiven by the above-noted 20-byte signature. The hash digest may berepresented by a corresponding “hash handle,” which in some cases maycomprise a particular portion of the hash digest. The hash handleillustratively maps on a one-to-one basis to the corresponding full hashdigest within a designated cluster boundary or other specified storageresource boundary of a given storage system. In arrangements of thistype, the hash handle provides a lightweight mechanism for uniquelyidentifying the corresponding full hash digest and its associated datapage within the specified storage resource boundary. The hash digest andhash handle are both considered examples of “content-based signatures”as that term is broadly used herein.

Examples of techniques for generating and processing hash handles forrespective hash digests of respective data pages are disclosed in U.S.Pat. No. 9,208,162, entitled “Generating a Short Hash Handle,” and U.S.Pat. No. 9,286,003, entitled “Method and Apparatus for Creating a ShortHash Handle Highly Correlated with a Globally-Unique Hash Signature,”both of which are incorporated by reference herein.

As mentioned previously, storage controller components in an XtremIO™storage array illustratively include C-module, D-module and R-modulecomponents. For example, separate instances of such components can beassociated with each of a plurality of compute nodes in a clusteredstorage system implementation.

The distributed storage controller in this example is configured togroup consecutive pages into page groups, to arrange the page groupsinto stripes, to arrange stripes into stripe ranges and to assign thestripes and stripe ranges to different ones of the C-modules. Forexample, if there are 1024 stripes distributed evenly across theC-modules, and there are a total of 16 C-modules in a givenimplementation, each of the C-modules “owns” 1024/16=64 stripes. In sucharrangements, different ones of the stripes are assigned to differentones of the control modules 808C such that control of the stripes withinthe storage controller 808 of the storage system 805 is substantiallyevenly distributed over the control modules 808C of the storagecontroller 808.

The D-module 808D of the storage controller 808 interfaces with acapacity module 814J of the enclosure controller 814 which allows a userto locate a given user data page based on its signature. For example,the D-module 808D receives instructions from the C-module 808C, e.g.,aggregated write cache entries, and determines whether they are writeoperations, read operations, increment operations, decrement operationsor fused operations. The D-module then submits the operation as an APIoperation to the enclosure controller 814, e.g., to capacity module814J. The enclosure controller 814 then performs the necessary RAIDoperations, mapping, etc. to either write or obtain the correspondingdata to the data storage devices 810 and to update the correspondingmetadata in the metadata storage devices 812 if necessary.

Each metadata page also has a size of 8 KB and includes multipleinstances of the <lun_id, offset, signature> for respective ones of aplurality of the user data pages. Such metadata pages are illustrativelygenerated by the capacity module 814J but are accessed by the D-moduleusing the capacity module 814J based on a metadata page signature.

The metadata page signature in this embodiment is a 20-byte signaturebut is not based on the content of the metadata page. Instead, themetadata page signature is generated based on an 8-byte metadata pageidentifier that is a function of the LUN identifier and offsetinformation of that metadata page.

If a user wants to read a user data page having a particular LUNidentifier and offset, the corresponding metadata page identifier isfirst determined, then the metadata page signature is computed for theidentified metadata page and submitted to the enclosure controller. Theenclosure controller then reads the corresponding metadata page usingthe computed signature. In this embodiment, the metadata page signatureis more particularly computed using a signature generation algorithmthat generates the signature to include a hash of the 8-byte metadatapage identifier, one or more ASCII codes for particular predeterminedcharacters, as well as possible additional fields. The last bit of themetadata page signature may always be set to a particular logic value soas to distinguish it from the user data page signature in which the lastbit may always be set to the opposite logic value.

The metadata page signature is used to retrieve the metadata page viathe D-module 808D of the storage controller 808 and capacity module814J. This metadata page will include the <lun_id, offset, signature>for the user data page if the user page exists. The signature of theuser data page is then used to retrieve that user data page, also viathe D-module and capacity module 814J.

Write requests processed in the content addressable storage system 805each illustratively comprise one or more IO operations directing that atleast one data item of the storage system 805 be written to in aparticular manner. A given write request is illustratively received inthe storage system 805 from a host device, illustratively one of thehost devices 102. In some embodiments, a write request is received inthe distributed storage controller 808 of the storage system 805 anddirected from one processing module to another processing module of thedistributed storage controller 808. For example, a received writerequest may be directed from a routing module 808R of the distributedstorage controller 808 to a particular control module 808C of thedistributed storage controller 808. Other arrangements for receiving andprocessing write requests from one or more host devices can be used.

The term “write request” as used herein is intended to be broadlyconstrued, so as to encompass one or more IO operations directing thatat least one data item of a storage system be written to in a particularmanner. A given write request is illustratively received in a storagesystem from a host device.

In the XtremIO™ context, the C-modules, D-modules and R-modules of thecompute nodes 815 communicate with one another over a high-speedinternal network such as an InfiniBand network. The C-modules, D-modulesand R-modules coordinate with one another to accomplish various IOprocessing tasks.

The write requests from the host devices identify particular data pagesto be written in the storage system 805 by their corresponding logicaladdresses each comprising a LUN ID and an offset.

As noted above, a given one of the content-based signaturesillustratively comprises a hash digest of the corresponding data page,with the hash digest being generated by applying a hash function to thecontent of that data page. The hash digest may be uniquely representedwithin a given storage resource boundary by a corresponding hash handle.

The storage system 805 utilizes a two-level mapping process to maplogical block addresses to physical block addresses. The first level ofmapping uses an address-to-hash (“A2H”) table and the second level ofmapping uses a hash metadata (“HMD”) table, with the A2H and HMD tablescorresponding to respective logical and physical layers of thecontent-based signature mapping within the storage system 805.

The first level of mapping using the A2H table associates logicaladdresses of respective data pages with respective content-basedsignatures of those data pages. This is also referred to logical layermapping. In illustrative embodiments, the A2H table and mapping ismanaged by the storage controller 808.

The second level of mapping using the HMD table associates respectiveones of the content-based signatures with respective physical storagelocations in one or more of the storage devices 810. This is alsoreferred to as physical layer mapping. In illustrative embodiments, theHMD table and mapping is managed by the enclosure controller 814.

For a given write request, both of the corresponding HMD and A2H tablesare updated in conjunction with the processing of that write request.

The A2H and HMD tables described above are examples of what are moregenerally referred to herein as “mapping tables” of respective first andsecond distinct types. Other types and arrangements of mapping tables orother content-based signature mapping information may be used in otherembodiments.

The logical block addresses or LBAs of a logical layer of the storagesystem 805 correspond to respective physical blocks of a physical layerof the storage system 805. The user data pages of the logical layer areorganized by LBA and have reference via respective content-basedsignatures to particular physical blocks of the physical layer.

Each of the physical blocks has an associated reference count that ismaintained within the storage system 805. For example, the referencecounts may be maintained in the metadata storage devices 812. Thereference count for a given physical block indicates the number oflogical blocks that point to that same physical block.

In releasing logical address space in the storage system, adereferencing operation is generally executed for each of the LBAs beingreleased. More particularly, the reference count of the correspondingphysical block is decremented. A reference count of zero indicates thatthere are no longer any logical blocks that reference the correspondingphysical block, and so that physical block can be released.

It should also be understood that the particular arrangement of storagecontroller processing modules 808C, 808D, 808R and 808M and enclosurecontroller capacity module 814J as shown in the FIG. 8 embodiment ispresented by way of example only. Numerous alternative arrangements ofprocessing modules of a distributed storage controller and capacitymodules of enclosure controllers may be used to implement functionalityfor offloading processing to a disk array enclosure in a clusteredstorage system in other embodiments.

Additional examples of content addressable storage functionalityimplemented in some embodiments by control modules 808C, data modules808D, routing modules 808R and management module(s) 808M of distributedstorage controller 808 can be found in U.S. Pat. No. 9,104,326, entitled“Scalable Block Data Storage Using Content Addressing,” which isincorporated by reference herein. Alternative arrangements of these andother storage node processing modules of a distributed storagecontroller in a content addressable storage system can be used in otherembodiments.

Illustrative embodiments of host devices or storage systems withfunctionality for offloading can provide a number of significantadvantages relative to conventional arrangements. For example, someembodiments provide techniques for offloading that reduce the processingthat is required to be performed by the storage controller and reducethe amount of bandwidth usage between the storage controller and thedisk array enclosure. These techniques allow the storage controller tofree up processing resources and bandwidth for use in servicingadditional 10 requests or other system needs while the enclosurecontroller handles the RAID and mapping tasks.

It is to be appreciated that the particular advantages described aboveand elsewhere herein are associated with particular illustrativeembodiments and need not be present in other embodiments. Also, theparticular types of information processing system features andfunctionality as illustrated in the drawings and described above areexemplary only, and numerous other arrangements may be used in otherembodiments.

Illustrative embodiments of processing platforms utilized to implementhost devices and storage systems with functionality for offloading willnow be described in greater detail with reference to FIGS. 9 and 10.Although described in the context of system 100, these platforms mayalso be used to implement at least portions of other informationprocessing systems in other embodiments.

FIG. 9 shows an example processing platform comprising cloudinfrastructure 900. The cloud infrastructure 900 comprises a combinationof physical and virtual processing resources that may be utilized toimplement at least a portion of the information processing system 100.The cloud infrastructure 900 comprises multiple virtual machines (VMs)and/or container sets 902-1, 902-2, . . . 902-L implemented usingvirtualization infrastructure 904. The virtualization infrastructure 904runs on physical infrastructure 905, and illustratively comprises one ormore hypervisors and/or operating system level virtualizationinfrastructure. The operating system level virtualization infrastructureillustratively comprises kernel control groups of a Linux operatingsystem or other type of operating system.

The cloud infrastructure 900 further comprises sets of applications910-1, 910-2, . . . 910-L running on respective ones of theVMs/container sets 902-1, 902-2, . . . 902-L under the control of thevirtualization infrastructure 904. The VMs/container sets 902 maycomprise respective VMs, respective sets of one or more containers, orrespective sets of one or more containers running in VMs.

In some implementations of the FIG. 9 embodiment, the VMs/container sets902 comprise respective VMs implemented using virtualizationinfrastructure 904 that comprises at least one hypervisor. Suchimplementations can provide functionality for offloading of the typedescribed above for one or more processes running on a given one of theVMs. For example, each of the VMs can implement such functionality forone or more processes running on that particular VM.

An example of a hypervisor platform that may be used to implement ahypervisor within the virtualization infrastructure 904 is the VMware®vSphere® which may have an associated virtual infrastructure managementsystem such as the VMware® vCenter™. The underlying physical machinesmay comprise one or more distributed processing platforms that includeone or more storage systems.

In other implementations of the FIG. 9 embodiment, the VMs/containersets 902 comprise respective containers implemented using virtualizationinfrastructure 904 that provides operating system level virtualizationfunctionality, such as support for Docker containers running on baremetal hosts, or Docker containers running on VMs. The containers areillustratively implemented using respective kernel control groups of theoperating system. Such implementations can provide functionality foroffloading of the type described above for one or more processes runningon different ones of the containers. For example, a container hostdevice supporting multiple containers of one or more container sets canimplement one or more instances of such functionality or logic.

As is apparent from the above, one or more of the processing modules orother components of system 100 may each run on a computer, server,storage device or other processing platform element. A given suchelement may be viewed as an example of what is more generally referredto herein as a “processing device.” The cloud infrastructure 900 shownin FIG. 9 may represent at least a portion of one processing platform.Another example of such a processing platform is processing platform1000 shown in FIG. 10.

The processing platform 1000 in this embodiment comprises a portion ofsystem 100 and includes a plurality of processing devices, denoted1002-1, 1002-2, 1002-3, . . . 1002-K, which communicate with one anotherover a network 1004.

The network 1004 may comprise any type of network, including by way ofexample a global computer network such as the Internet, a WAN, a LAN, asatellite network, a telephone or cable network, a cellular network, awireless network such as a WiFi or WiMAX network, or various portions orcombinations of these and other types of networks.

The processing device 1002-1 in the processing platform 1000 comprises aprocessor 1010 coupled to a memory 1012.

The processor 1010 may comprise a microprocessor, a microcontroller, anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA) or other type of processing circuitry, as well asportions or combinations of such circuitry elements.

The memory 1012 may comprise random access memory (RAM), read-onlymemory (ROM), flash memory or other types of memory, in any combination.The memory 1012 and other memories disclosed herein should be viewed asillustrative examples of what are more generally referred to as“processor-readable storage media” storing executable program code ofone or more software programs.

Articles of manufacture comprising such processor-readable storage mediaare considered illustrative embodiments. A given such article ofmanufacture may comprise, for example, a storage array, a storage diskor an integrated circuit containing RAM, ROM, flash memory or otherelectronic memory, or any of a wide variety of other types of computerprogram products. The term “article of manufacture” as used hereinshould be understood to exclude transitory, propagating signals.Numerous other types of computer program products comprisingprocessor-readable storage media can be used.

Also included in the processing device 1002-1 is network interfacecircuitry 1014, which is used to interface the processing device withthe network 1004 and other system components and may compriseconventional transceivers.

The other processing devices 1002 of the processing platform 1000 areassumed to be configured in a manner similar to that shown forprocessing device 1002-1 in the figure.

Again, the particular processing platform 1000 shown in the figure ispresented by way of example only, and system 100 may include additionalor alternative processing platforms, as well as numerous distinctprocessing platforms in any combination, with each such platformcomprising one or more computers, servers, storage devices or otherprocessing devices.

For example, other processing platforms used to implement illustrativeembodiments can comprise converged infrastructure such as VxRail™,VxRack™, VxRack™ FLEX, VxBlock™ or Vblock® converged infrastructure fromVCE, the Virtual Computing Environment Company, now the ConvergedPlatform and Solutions Division of Dell EMC.

It should therefore be understood that in other embodiments differentarrangements of additional or alternative elements may be used. At leasta subset of these elements may be collectively implemented on a commonprocessing platform, or each such element may be implemented on aseparate processing platform.

As indicated previously, components of an information processing systemas disclosed herein can be implemented at least in part in the form ofone or more software programs stored in memory and executed by aprocessor of a processing device. For example, at least portions of thefunctionality for offloading as disclosed herein are illustrativelyimplemented in the form of software running on one or more processingdevices.

It should again be emphasized that the above-described embodiments arepresented for purposes of illustration only. Many variations and otheralternative embodiments may be used. For example, the disclosedtechniques are applicable to a wide variety of other types ofinformation processing systems, host devices, storage systems, computenodes, capacity nodes, storage devices, storage controllers, disk arrayenclosures or enclosure controllers, etc. Also, the particularconfigurations of system and device elements and associated processingoperations illustratively shown in the drawings can be varied in otherembodiments. Moreover, the various assumptions made above in the courseof describing the illustrative embodiments should also be viewed asexemplary rather than as requirements or limitations of the disclosure.Numerous other alternative embodiments within the scope of the appendedclaims will be readily apparent to those skilled in the art.

What is claimed is:
 1. An apparatus comprising: a storage systemcomprising a disk array enclosure, the disk array enclosure comprising:at least one enclosure controller comprising at least one processingdevice coupled to memory; a cache comprising a metadata journal; aplurality of data storage devices in communication with the at least oneenclosure controller; and a plurality of metadata storage devices incommunication with the at least one enclosure controller, each metadatastorage device being configured to store metadata corresponding to datastored on the plurality of storage devices; wherein the at least oneenclosure controller is configured: to write a stripe metadata page tothe metadata storage devices, the stripe metadata page corresponding toa stripe of data stored on the plurality of data storage devices of thedisk array enclosure; to determine that the write of the stripe metadatapage failed for a first metadata storage device of the plurality ofmetadata storage devices; to add an entry to the metadata journal basedat least in part on the determination that the write of the stripemetadata page failed, the entry comprising an indication of the firstmetadata storage device and an indication of the stripe of data; and toset an indication in a data structure associated with the disk arrayenclosure that the stripe metadata page for the stripe of data has notbeen written to the first metadata storage device.
 2. The apparatus ofclaim 1 wherein the at least one enclosure controller is furtherconfigured: to determine that the write of the stripe metadata pagesucceeded for a second metadata storage device of the plurality ofmetadata storage devices; to determine that the metadata journalcomprises a second entry corresponding to the second metadata storagedevice, the second entry comprising an indication of the second metadatastorage device and an indication of the stripe of data; and toinvalidate the second entry in the metadata journal based at least inpart on the determination that the write of the stripe metadata pagesucceeded for the second metadata storage device.
 3. The apparatus ofclaim 1 wherein the memory comprises a dirty data structure associatedwith the first metadata storage device, the at least one enclosurecontroller being further configured to add an entry to the dirty datastructure based at least in part on the determination that the write ofthe stripe metadata page failed for the first metadata storage device,the entry added to the dirty data structure comprising a logicalidentifier corresponding to at least a portion of the stripe of data. 4.The apparatus of claim 3 wherein the at least one enclosure controlleris further configured: to receive a read operation comprising thelogical identifier; to determine that the dirty data structureassociated with the first metadata storage device comprises the logicalidentifier; and to attempt to obtain the stripe metadata page fromanother of the plurality of metadata storage devices based at least inpart on the determination that the dirty data structure associated withthe first metadata storage device comprises the logical identifier. 5.The apparatus of claim 4 wherein: the memory comprises a plurality ofdirty data structures each associated with a corresponding metadatastorage device of the plurality of metadata storage devices; the atleast one enclosure controller is further configured: to maintain a copyof the stripe metadata page on the plurality of data storage devices; todetermine that each of the dirty data structures comprises the logicalidentifier; and to obtain the stripe metadata page from the plurality ofdata storage devices based at least in part on the determination thatthe each of the dirty data structures comprises the logical identifier.6. The apparatus of claim 4 wherein the at least one enclosurecontroller is further configured: to determine that the attempt toobtain the stripe metadata page from the another of the plurality ofmetadata storage devices was successful; and to copy the stripe metadatapage to the first metadata storage device based at least in part on thedetermination that the attempt to obtain the stripe metadata page wassuccessful.
 7. The apparatus of claim 1 wherein the stripe metadata pageis a first stripe metadata page and wherein the at least one enclosurecontroller is further configured: to set the first metadata storagedevice to a hiccup state based at least in part on the determinationthat the write of the first stripe metadata page failed for the firstmetadata storage device; and to add a second entry to the metadatajournal for an attempted write of a second stripe metadata page to thefirst metadata storage device based at least in part on the firstmetadata storage device being in the hiccup state.
 8. The apparatus ofclaim 7 wherein in response to an attempted read of the second stripemetadata page from the first metadata storage device while the firstmetadata storage device is in the hiccup state, the at least oneenclosure controller is further configured to read the second stripemetadata page from another of the metadata storage devices.
 9. Theapparatus of claim 7 wherein the at least one enclosure controller isfurther configured: to determine that a threshold criterion is met bythe first metadata storage device; to set the first metadata storagedevice to a healthy state based at least in part on the determinationthat the threshold criterion is met by the first metadata storagedevice; and to resynchronize the first metadata storage device based atleast in part on the determination that the threshold criterion is metby the first metadata storage device.
 10. The apparatus of claim 9wherein resynchronizing the first metadata storage device comprises: foreach entry corresponding to the first metadata storage device in themetadata journal: reading a valid copy of the corresponding stripemetadata page from another of the metadata storage devices; writing thevalid copy of the corresponding stripe metadata page to the firstmetadata storage device; and invalidating the entry in the metadatajournal.
 11. A method comprising: writing a stripe metadata page to aplurality of metadata storage devices of a disk array enclosure, thestripe metadata page corresponding to a stripe of data stored on aplurality of data storage devices of the disk array enclosure;determining that the write of the stripe metadata page failed for afirst metadata storage device of the plurality of metadata storagedevices; adding an entry to a metadata journal stored in a cache of thedisk array enclosure based at least in part on the determination thatthe write of the stripe metadata page failed, the entry comprising anindication of the first metadata storage device and an indication of thestripe of data; and setting an indication in a data structure associatedwith the disk array enclosure that the stripe metadata page for thestripe of data has not been written to the first metadata storagedevice; wherein the method is implemented by at least one enclosurecontroller of the disk array enclosure.
 12. The method of claim 11wherein the method further comprises: determining that the write of thestripe metadata page succeeded for a second metadata storage device ofthe plurality of metadata storage devices; determining that the metadatajournal comprises a second entry corresponding to the second metadatastorage device, the second entry comprising an indication of the secondmetadata storage device and an indication of the stripe of data; andinvalidating the second entry in the metadata journal based at least inpart on the determination that the write of the stripe metadata pagesucceeded for the second metadata storage device.
 13. The method ofclaim 11 wherein the at least one enclosure controller comprises atleast one processing device coupled to memory, the memory comprising adirty data structure associated with the first metadata storage device,the method further comprising adding an entry to the dirty datastructure based at least in part on the determination that the write ofthe stripe metadata page failed for the first metadata storage device,the entry added to the dirty data structure comprising a logicalidentifier corresponding to at least a portion of the stripe of data.14. The method of claim 13 wherein the method further comprises:receiving a read operation comprising the logical identifier;determining that the dirty data structure associated with the firstmetadata storage device comprises the logical identifier; and attemptingto obtain the stripe metadata page from another of the plurality ofmetadata storage devices based at least in part on the determinationthat the dirty data structure associated with the first metadata storagedevice comprises the logical identifier.
 15. The method of claim 14wherein: the memory comprises a plurality of dirty data structures eachassociated with a corresponding metadata storage device of the pluralityof metadata storage devices; the method further comprises: maintaining acopy of the stripe metadata page on the plurality of data storagedevices; determining that each of the dirty data structures comprisesthe logical identifier; and obtaining the stripe metadata page from theplurality of data storage devices based at least in part on thedetermination that the each of the dirty data structures comprises thelogical identifier.
 16. The method of claim 14 wherein the methodfurther comprises: determining that the attempt to obtain the stripemetadata page from the another of the plurality of metadata storagedevices was successful; and copying the stripe metadata page to thefirst metadata storage device based at least in part on thedetermination that the attempt to obtain the stripe metadata page wassuccessful.
 17. The method of claim 11 wherein the stripe metadata pageis a first stripe metadata page and wherein the method furthercomprises: setting the first metadata storage device to a hiccup statebased at least in part on the determination that the write of the firststripe metadata page failed for the first metadata storage device; andadding a second entry to the metadata journal for an attempted write ofa second stripe metadata page to the first metadata storage device basedat least in part on the first metadata storage device being in thehiccup state.
 18. The method of claim 17 wherein in response to anattempted read of the second stripe metadata page from the firstmetadata storage device while the first metadata storage device is inthe hiccup state, the method further comprises reading the second stripemetadata page from another of the metadata storage devices.
 19. Themethod of claim 17 wherein the method further comprises: determiningthat a threshold criterion is met by the first metadata storage device;setting the first metadata storage device to a healthy state based atleast in part on the determination that the threshold criterion is metby the first metadata storage device; and resynchronizing the firstmetadata storage device based at least in part on the determination thatthe threshold criterion is met by the first metadata storage device, theresynchronizing comprising: for each entry corresponding to the firstmetadata storage device in the metadata journal: reading a valid copy ofthe corresponding stripe metadata page from another of the metadatastorage devices; writing the valid copy of the corresponding stripemetadata page to the first metadata storage device; and invalidating theentry in the metadata journal.
 20. A computer program product comprisinga non-transitory processor-readable storage medium having stored thereinprogram code of one or more software programs, the program code whenexecuted by at least one enclosure controller of a disk array enclosureof a storage system, causes the at least one enclosure controller: towrite a stripe metadata page to a plurality of metadata storage devicesof the disk array enclosure, the stripe metadata page corresponding to astripe of data stored on a plurality of data storage devices of the diskarray enclosure; to determine that the write of the stripe metadata pagefailed for a first metadata storage device of the plurality of metadatastorage devices; to add an entry to a metadata journal stored in a cacheof the disk array enclosure based at least in part on the determinationthat the write of the stripe metadata page failed, the entry comprisingan indication of the metadata storage device and an indication of thestripe of data; and to set an indication in a data structure associatedwith the disk array enclosure that the stripe metadata page for thestripe of data has not been written to the first metadata storagedevice.